1. Field of the Invention
The invention relates to high liquid level detection system and, more specifically, to high level alarm system in a wet well.
2. Description of Related Art
Throughout the world sanitary sewer collection systems utilize gravity flow to direct wastewater to water reclamation plants. Many times the waste water cannot move via gravity the entire distance to a water reclamation plant, and it must be pumped up to higher elevations to continue its gravity flow to the water reclamation plant. During these pumping steps, wastewater is temporarily contained in low point tanks called wet wells. These wet wells have pumps that occasionally pump the wastewater toward the reclamation plant. The pumps and their associated controls are located at the wet wells and are powered by utility provided alternate current (AC) power. When there is a failure of AC power (for a variety of reasons) the wet well pumps and their associated controls cannot operate. Some pump stations have standby generators to operate the pumps in such outages, but many do not. Therefore, during AC outages no pumping can occur. However, during such AC outages, waste water flow continues into the wet well and, therefore, during AC outages there is a much higher likelihood of high wet well situations, which if unresolved, will result in a waste water spill into the general environment.
Generally, the wet wells are equipped with high-level alarm floats that detect high level situations. During these situations as the wastewater continues to rise in the wet well the high-level alarm floats are reached and tipped by the wastewater. When a float tips, a mercury type switch inside the float completes a circuit, which, if there were AC power, would energize a relay, which in turn would energize a local alarm circuit. This high wet well relay would also indicate an alarm to a separate (optional) alarm monitoring system that would transmit (via a plurality of means) the alarms to an entity(s) off site.
Some times a separate high level float is installed at the pump station and is connected directly to the alarm system. This is problem for two reasons. First, it is typically difficult to “pull” another high level float as the conduit from the wet well to the control panel is sealed to prevent gases from entering the control panel, thereby requiring excessive installation time. Second, the second high level float adds cost and can interfere with the original high level float. Since there is no local AC power this local and off site alarming does not occur in case of AC power failure. Additionally, retrofitting an alarm or monitoring system to an existing pump station control panel can be difficult and demand additional auxiliary/interposing relays, which the existing control panel may not be able to accommodate from a physical size stand point.
Accordingly, it would be advantageous to provide a system that provides a better way for monitoring high level in a wet well.